Objectives: The aim of the present study was to compare the performance of the vertical jump task and the level of disability between the coper and non-coper athletes with an anterior cruciate ligament-minus knee.

Methods: Thirty-four professional male athletes with isolated complete anterior cruciate ligament-tear (age 20-29 years and 6-12 months time past injury) were recruited in this study. The subjects were allocated into the coper (n=17) and non-coper (n=17) groups according to their history of having giving way and feeling an instability in their injured knee. The maximum vertical jump height was recorded by a 6-camera Vicon motion analysis system. The functional outcomes of the subjects were assessed with use of the Persian versions of the International Knee Documentation Committee, Knee Injury and Osteoarthritis Outcome Score and Tegner Questionnaires.

Results: The results revealed that the coper ACK-deficient knee subjects had a significantly higher International Knee Documentation Committee score as well as two subscales of the KOOS questionnaire including the sports (P=0.001) and the quality of life (P=0.016) than non-copers. However, the subscales of pain (P=0.0137), symptoms (P=0.353) and the activities of daily living (P=0.133) of the KOOS questionnaire did not show any significant differences between the coper and non-coper ACL-deficient knee subjects. In addition, the maximum jumping height was significantly higher in the copers too (P=0.008).

Discussion: While the pain, symptoms and daily activities were not different between the two groups, a higher level of the functional abilities, sports activities, quality of life and the maximum jumping height were shown in the coper ACL-deficient knee subjects when compared to the non-copers. A deliberate evaluation of the functional abilities in ACL-deficient knee subjects might play a key role in distinguishing the coper and non-coper ACL-deficient knee subjects.